Luminescent material



Patented June 17, 1941 LUMESCENT MATERIAL Ludwig Wesch, Heidelberg,Germany, assignor to 'Telefnnken Gesellsehaft flir- DrahtloseTelegraphie m. b. 11., Berlin, Germany, a c

Germany tion of No Drawing. Application June 13, 1939, Serial No.

In Germany March 26, 1938 11 Claims. (CL 250-81) The invention relates,to the manufacture of luminescent materials or phosphors used to convertor transduce radiant energy of ultra-violet,

X-ray, cathode-ray or other radiations .into visible light.

Most of the methods known in the art resort to the sinter furnace tomake phosphors at high temperatures. The raw materials are mixed withactivating metals and the mixture is placed in a crucible which isplaced in a'furnace in which the production of the phosphor is completedwithin a fixed period of, time and at predetermined temperatures. Afterthe heating treat- I ment, the content of the crucible is finely groundand reheated in case there has been destruction 7 of the luminescentproperties by the grinding.

emitted radiation in a thinlayer or film should be equal to one.

- Now, the invention is predicated upon a proper appreciation of thefact that the actual impairment or loss of emciency of conversion isascribable to the circumstancethat the total raw material in'the courseof the sintering process does not acquire luminous centers, with theresult that a major portion of the material does not become activatedand merely has an absorbing action. Moreover, because of the thicknessor the depth of the layers of luminescent material customarily employedin practice, there is occasioned an essential loss or diminution of theemitted light inside the pulverulent phosphor. The maximum thickness ofa layer of these substances which is still pervious to the excitingenergy is around .05 mm., and the result is that the whole phosphors.More particularly speaking, such phosphors shall be made accessible andbe opened up to technological uses whose dielectric constant experiencesalterations when irradiated by light, in other words, substances whichare adapted to a conversion of luminous energy into frequency variationsof a transmitter as known in the art.

According to the invention, the starting materials or raw materials ofphosphors which are rid of activating metals, are mixed and fused toresuit in plates or slabs of phosphors whose activation is accomplishedby causing the activating metallic agent to migrat into the phosphorplate by thermal and/or electrolytic ways and means.

By the thermal or electrolytic migration of the activating metal intothe phosphor plate or sheet according to the invention there results aperfectly uniform distribution of the activator inside the phosphormatrix or base so that, contradictinct to the prior art, no essentialpart of the starting material will remain inactive so far as luminousconversion is concerned. The plate thus consists purely of uniformlydivided phosphor or luminescent centers, without the presence of any"filler." Moreover, the invention constitutes an essential progressbecause .of the reduction of the coefficient of absorption (orabsorptivity) of the material for fluorescent or phosphorescent lightfor the reason that the material is completely transparent, orpractically so. While in the case of phosphor powders it would beuseless to raise the depth or thickness of the coat or layer beyond theM -mm. mark. on the ground that no more light would reach the vsurfacefrom greater depths it is now possible to obtain a greater luminousdensity on the surface because it is now feasible to use heavier layers,seeing that light rising from greater depths hardly suffers anyabsorption.

By utilizing the entire basic or matrix material, and by-reducing theabsorptivity according to the invention, the field of application of thematerial is greatly expanded. Amoiig the uses to which the improvedscreens and material may be placed are luminous numbers, dials, clocksand watches (time pieces), etc.; moreover, the uses in Roentgenology andin television apparatus prediused for the re-creation of pictures onlumlnescent screens, this must conduce to a lack of sharpness, that is,to blur.

Now, the aim and purpose of the invention is to raise the efiiciency byobviating the above named difficulties, to the end of therebyencatedupon the use of cathode-raysin the form of luminescent screens,luminescent foils, as the active material in a condenser, etc. willresult in improved efllciency and effects.

. Examining, for example, a luminescent screen a of the kind used intelevision apparatus, it will be found that the picture is re-createdupon the larging the technical and commercial utility of posterior face,while it is viewed from the front.

millimeter without suflfering relatively appre-v ciable losses inluminescence or luminosity.

By my invention all of these shortcomings are obviated. For such light,as is caused by cathode-rays, reaches the surface undiminished inintensity: there is no scatter by the granulated phosphor, while actionsby the filler or grain size itself are absent since a body or substanceresembling glass is dealt with, which is uniformly activated by theactivating centers, the distance between centers in the body probablybeing somewhatgreater than the cross-section of action of a .center,that is, 5x10 mm. Even under maximum magnification, this raster or thegrain size will not 'become appreciable. What has here been statedrespecting the use of the material in the television art, holds true,

a fortiori, also in the case of luminescent screens employed inroentgenology.

Accordingly, it will be appreciated that one of the main objects of myinvention is to provide an improved luminescent material and screentogether with a method for providing such screens and materials.

A further object of my invention is to provide a new method foractivating luminescent materials to increase their efliciency.

Another object of my invention is to provide an electrolytic method foractivating luminescent materials more uniformly.

Still another object of my invention is to provide a luminescent screenwhich shall be free from granular structure to increase lighttransmission efiiciency and to provide a screen which preserves maximumamount of detail in reproduction'of television images.

Other objects and advantages of my invention will become clear from areading of the following detailed description.

The method of the invention comprises the following steps or stages: Thestarting or raw materials such as sulfides, selenides, tellurides,oxides, carbonates, silicates, zirconates, titanates, molybdates,tungstates, borates, etc., are fused in an annealing furnace into aclear melt and/or crystallized, optionally in the presence of highpressures. To insure higher conductivity, if desired, salts may be usedof a kind capable of increasing the conductivity. However, the basic orstarting materials should be free from activating metals. After meltingto result in a desired form, or else after shaping the molten startingmaterial, the articles or objects made of the starting material, beingmore or less transmitting or pervious to light, are then given a perfectpolish. After the polishing, either by chemical or by physicaltreatment, the activating material is deposited or precipitated upon theensuing article. The most suitable way of accomplishing this is byvaporizing the metal on the surface 'in vacuo. After the metallized coator film has thus ,been uniformly applied,'

the positive and the negative poles of a source of potential supply(battery), though care must be taken so that between opposite sides ofthe article there will be no conducting particles of metal. Next, thebody thus pre-treated is placed into an annealing furnace or leer,which, for the sakeJof more efficient temperature control is heatedelectrically, with voltage being impressed upon the metal electrodes. Asa result of the rise of temperature, the body of starting materialwhich, at ordinary temperature hardly conducts current, is changed intoa better conductor, while from one of the electrodes which consists ofactivating metal, metallic ions migrate into the basic material with theconsequence that within a relatively large surface and depth of thelayer, the activating metallic atoms will come to permeate the body inperfect uniformity as a result of the potential difference. After adefinite quantity of electricity which is measurable by means of amilli-ammeter has flowed through the body' with an incidental mlgrationof the desired number of metallic ions, the current is disconnected andthe desired light accumulator or light transformer or transducer isfinished. If desired, it may be treated further by moderate annealing orglowing. Cooling may be effected at a high or a low rate, according towhether relatively great phosphorescence or fluorescence is wanted. Forself-excitation, also radium or radium-bearing compounds may beincorporated in all bodies. I

In what follows, a few examples shall be cited to illustrate the waysand means adapted to carry the invention into practice: (1) 10 grams39.003 and 3 grams NaCl are fused to result in a tenuous plate or sheet.This plate is then polished. After polishing, a silver coating byvaporization is applied upon both faces by the aid of cathode spatter ordisintegration. After placingthe plate onto an electric furnace andheating at 800 degrees C., a voltage of 220 v. is impressed upon theplate. After two hours, the current is cut oil and the finishedluminescent plate is taken out of the furnace, is allowed to cool toordinary temperature, and the silver is removed by grinding. Thethickness ofthe experimental plate thus formed was 1 mm. and weighed 8grams. (2) 50 grams of ZnS and 5 grams of Mel: are fused in ahigh-pressure furn'ace in the presence of nitrogen to result in aopposite points of the article are connected with clear plate. This isfollowed by polishing and application of a copper film. To insure betterterminal conditions, a copper electrode is laid upon the metallizedsurface. Next, the plate is placed into an electric furnace and voltageis applied.

Potential volts 1600 Temperature degrees C 950 Length of annealing hours4 Thickness of plate mm 1 Yield --grams 40 (3) 100 grams Zl'izSlO-i and10 grams LiCl are molten at 1600 degrees C. to result in a perfectlyclear melt,'the latter being cast into a plate. Deposited upon thepolished faces are films of neodymium. After removal of the currentlead, the plate is brought into the furnace and potential is applied.

Potential volts 2000 Temperature -degrees C 1050 Length of heating"hours" 6 Thickness of plate mm 1 Yield ..grams a plate. copper coatsare deposited, the copper containing radium at the rate of 1 10- gramper'gram After an annealing time of 6 hours, the voltage is removed. Theplate is allowed to cool down to 400 degrees during 4 hours; the plateis then taken out of the furnace and allowed to cool to roomtemperature.

(4) 100 grams ZNO BaO (S102): and 10 grams LiCl are fused at 1600degrees C. and cast into Upon the polished faces of the plate copper.After placing the plate into an 'electrical furnace, potential isapplied.

At the end of the heating period, voltage is removed followed bytempering at 500 degrees for four hours and cooling to room temperature.

It will be understood that the invention is not confined to theprocedures hereinbefore described by way of example; in fact, it isapplicable and adapted to any kind of raw or starting material. Amongthe activating metals may be mentioned primarily copper, silver, or elseplatinum, yttrium, neodymium, etc. The invention moreover is usable inall light accumulators and light transducers as well as in connectionwith substances which alter their dielectric constant when illuminatedby light. What is here meant by light accumulators are substances whichare capable of converting violet, ultra-violet and X-ray light, furthercathode and radium rays, etc., into visible light, the light beingaccumulated or stored up and then re-emitted inside a relatively longperiod of time. What is here meant by light converters or transducersare substances which immediately convert violet, ultra-violet and X-raysand also cathode and radium radiations into visible light, withphosphoresence being invisible to the eye after removal ordiscontinuance of the irradiation.

' Having described my invention, what I claim is:

1. The method of activating luminescent materials which comprisesmelting component parts of the luminescent material, forming a platefrom the melted material, polishing at least one face of the formedplate, depositing a layer of activating metal upon the polished face,and electrolytically combining the deposited metal with the luminescentmaterial of the formed plate.

2. The method of activating luminescent materials which comprisesmelting component parts of the luminescent material, forming a platefrom the melted material, polishing at least one face of the formedplate, depositing a layer of activating metal upon the polished face,and thermally and electrolytically combining the deposited metal withthe luminescent material of the formed plate.

3. The method of activating luminescent materials which comprisesmelting component parts of the luminescent material, forming a platefrom the melted material, polishing at least one face of the formedplate, depositing a layer of activating metal upon the polished face,thermally and electrolytically combining the deposited metal with theluminescent material of the formed plate, and annealing the activatedlumi-' nescent material of the formed plate.

4. The method of activating luminescent ma terials which comprisesmelting component parts 75 of the luminescent material, forming a platefrom the melted material, polishing at least one face of the formedplate, depositing a layer of activating metal upon the polished face,and electrolytically combining the deposited metal with the luminescentmaterial of the formed plate.

5. The method of preparing an activated luminescent material screenwhich comprises melting component parts of the luminescent material,

' forming a plate from the melted material, polishing at least one faceof the formed plate, depositing a layer of activating metal upon thepolished face, electrolytically combining a portion of the depositedmetal with the luminescent material of the formed plate, andsubsequently removing from said face the uncombined portion of themetal.

6. The method of preparing an activated luminescent material screenwhich comprises melting component parts of the luminescent material,forming a plate from the melted material, polishing at least one face ofthe formed plate, depositing a layer of activating metal-upon thepolished face, and electrolytically combining a portion of the depositedmetal with the luminescent material of the formed plate, andsubsequently removing from said face the uncombined metal.

7. The method of preparing an activated luminescent material screenwhich comprises melting component parts of the luminescent material,farming a plate from the melted material, polishing at least one face ofthe formed plate, depositing a layer of activating metal upon thepolished face, and thermally and electrolytically combining a portion ofthe deposited metal with the luminescent material of the formed plate,and subsequently removing from said face the uncombined metal.

' 8. The method of preparing an activated luminescent material screenwhich comprises melting component parts of the luminescent material,forming'a plate from the melted material, polishing at least one face ofthe formed plate, clepositing a layer of activating metal upon the pol-5 ished face, thermally and electrolytically combining a portion of thedeposited metal with the luminescent material of the formed plate,removing from said face the uncombined metal and subsequently annealingthe activated luminescent material of the formed plate.

9. The method of preparing an activated luminescent plate whichcomprisesthe steps of fusing component parts of said luminescent plate,castv with said luminescent plate by applying electrical I potentialbetween thesaid metallic coatings, si-

- multaneously heating the transparent plate to a predeterminedtemperature for a predetermined time to give substantial increase inconductivity and uniform penetration of metallic ions from said portionof the coatings, removing the applied potential, and cooling the heatedplate.

10. The method of preparing an activated luminescent plate whichcomprises the steps of fusing component parts of said luminescent plate,casting the fused salts to form a transparent plate having two opposedfaces, polishing said facesof the formed plate, coating each of thepolished faces with a metallic layer, electrolytically combining aportion of said metallic coatings with said luminescent plate byapplying electrical po- WWW tential between said metallic layers,simultaneously heating the transparent plate'to a predeterminedtemperature for a predetermined time to give substantial increase inconductivity and uniform penetration of metallic ions from said portionof the coatings, removing the applied potential and cooling the heatedplate.

11. The method of preparing an activated luminescent plate whichcomprises the steps of fusing component parts of said luminescent plate,casting the fused salts to form a transparent plate having two opposedfaces, polishing said faces of the formed plate, coating each of thepolished faces with a metallic layer, electrolytically combining aportion of said metallic coatings with and substantially uniformpenetration of ions from said metallic layers throughout said plate,removing the applied potential, cooling the heat ed plate, andsubsequently removing from the iaces of said plate the uncombinedportion of the metallic layers.

LUDWIG WESCH.

